The range of methods that embed hidden data into entertainment signals are usually referred to as watermarking, regardless if these signals are originally created and/or distributed in the analog or digital form. They can be used to protect ownership rights associated with the entertainment signals so marked. This hidden data can also be used to provide the consumer with ancillary data associated with entertainment (audio, video or multimedia program) material being reproduced. Hidden information added to audio, video and other multimedia signals are called watermarks. Watermarked signals are used in the same way as their non-watermarked counterparts. For example, watermarked audio signals are typically played with their watermarks in place, such watermarks going undetected by the listener or viewer unless their playback equipment is fitted with apparatus to detect and reproduce the watermark data. Watermarks can also be detected and retrieved by the providers of the content, allowing these entities to perform a range of tasks including determining the holder or holders of the signal's copyright, verifying the authenticity of the entertainment signal, and determining the signal's place of origin.
To be effective, watermarking methods must not have a perceptible impact on signal quality. The level where perceptibility becomes problematic depends on the type of signal and its intended use. As a result, different watermarking methods may be appropriate for different signals and uses. Watermarking should also be tamper resistant. This means that watermarks must be difficult, if not impossible, to remove.
Most current watermarking systems embed information within signal portions that would be characterized (from the standpoint of perceptibility) as noise. This reduces the chance that embedded information will alter signals in a perceptible fashion. At the same time, such methods are often subject to tampering because it is generally possible to replace the noise-like portions of a signal with generated noise. This replacement effectively removes hidden watermark data with little or no degradation to signal quality. Based on the preceding, it may be appreciated that there is a need for improved tamper-resistant methods for watermarking entertainment signals.
Watermark data has been traditionally inserted at the time audio and/or video content is mastered. A watermark of this type is referred to as a source watermark. This watermark serves the content owners need to be able to track the original origin of the entertainment content. There is a second need to add hidden tracking, ancillary entertainment, and/or advertising data during the process of distributing the audio and video content to end users. A watermark of this type is referred to as a transaction watermark. This watermark identifies the distributor of the content and adds additional data to the content that is of use to the end user. There is a third need to add hidden data at the time of audio and video content playback by the end user. A watermark of this type is referred to as a fingerprint watermark. This hidden data relates to the rules of use associated with the reproduced entertainment stream as well as identification of the end user who played back the audio and/or video data. These rules of use may include the number of times this data stream can be subsequently copied as well as who has permission to perform such copying. The identification of the end user in the data streams can serve two purposes. One is to track a distributed data stream to determine if an end user violated the copyright holders rights. A second is to provide a means to reward the end user should he or she provide the data stream to a third party and the third party chooses to purchase an entertainment product from the content owner or distributor of the content.